Wednesday, December 2, 2009

Ph - acids and bases - igcse/gcse /chemistry notes

pH is a measure of how acidic or how alkaline a solution in water is.The pH scale goes from 1 to 14,with 1 being very strongly acidic,and 14 being very strongly alkaline.A pH of 7 is neutral.
You can measure the pH of a solution using universal indicator.Just as litmus paper will be red for an acid and blue for an alkali,so universal indicator is a mixture of indicatorswhich will give a different colour for a different pH.
Any acid will have a pH of less than 7.Any alkali will have a pH of more than 7.
A strong acid (HCl or H2SO4 or HNO3 )will have a pH of 1 (red).
A weak acid will have a pH of 3 to 4 (orange).Examples of weak acids are ethanoic acid (vinegar),citric acid (lemon juice) and rain water.
Rain water has a natural pH of 5·5 (see carbonic acid).
Water and salts are neutral, pH 7 (green).
A weak alkali (ammonia) will have a pH of 11 to 12 (blue).
A strong alkali (Ca(OH)2or NaOH) will have a pH of 14 (purple).

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